The present invention relates to processes for pickling metals with acid solutions containing hydrogen peroxide, and more particularly, it relates to methods for stabilizing hydrogen peroxide in such solutions, as well as to the solutions themselves.
It is known to use sulfuric acid baths containing hydrogen peroxide to pickle or clean metals. In the case of a divalent metal, M, the reaction occurs according to the following equation: EQU M+ H.sub.2 SO.sub.4 + H.sub.2 O.sub.2 .fwdarw. MSO.sub.4 + 2 H.sub.2 O
the hydrogen peroxide, however, is a material which is very sensitive to the presence of impurities which catalyse its decomposition. Among these impurities, metallic impurities are among the most active, and it is accordingly necessary to stabilize hydrogen peroxide-containing baths for pickling metals.
Among the additive materials proposed to stabilize the hydrogen peroxide in such baths are ethylene glycol and polyethylene glycols in British Patent 1,157,038 and French Patent 1,539,960; saturated aliphatic alcohols in U.S. Pat. No. 3,957,290; urea and its derivatives in British Patent 1,160,134; phenacetin and sulfathiazole in French Patent 1,427,149; and phenol in U.S. Pat. No. 3,649,194 and French Patent 2,065,380. Such prior art stabilizing agents used even up to the present time suffer a number of disadvantages. Thus, some of them are only slightly soluble in the pickling baths, while others complex the metal to be pickled. Yet others are toxic, while some of these prior art agents also inhibit or retard the pickling action of the baths.